1. Field of the Invention
The invention relates in general to a touch control system, and more particularly, to a pattern of sensing channels for connecting sensors and electrodes in a touch control system.
2. Description of the Related Art
Operating interfaces of recent electronic products have become increasingly user-friendly and intuitive with the progressing technology. For example, through a touch screen, a user can directly interact with applications and input messages/texts/patterns with fingers or a stylus, thus eliminating complexities associated with other input devices such as a keyboard or buttons. In practice, a touch screen usually comprises a touch panel and a display disposed at the back of the touch panel. According to a touch position on the touch panel and a currently displayed image on the display, an electronic device determines an intention of the touch to execute corresponding operations.
FIG. 1 shows a diagram of a configuration of electrodes/sensing channels of a self-capacitive touch panel. In a sensing region 100 marked by a dotted frame, a plurality of electrodes (e.g., electrodes 11A and 11B) having planar contours similar to right triangles are disposed. Each of the electrodes is connected to a sensing circuit (sensors 14A and 14B are depicted as representatives) on a flexible printed circuit board (FPC) 13 via a sensing channel (e.g., a sensing channel 12A or 12B). When the user touches the electrode 11A, for example, via the sensing channel 12A, a capacitance detected by the sensor 14A corresponding to the electrode 11A is changed. Accordingly, a subsequent circuit can determine that the user touch occurs at a position of the electrode 11A.
Ideally, it is preferred that resistances of the sensing channels toward the sensors are substantially equal. Thus, differences in time periods required for charging/discharging the sensors can be reduced to further lower inconsistencies in sensing results caused by circuit mismatch. However, as seen from FIG. 1, lengths of routes connecting the electrodes to the corresponding sensors are different. For example, the length of the sensing channel 12B connecting the electrode 11B is far greater than the length of the sensing channel 12A connecting the electrode 11A. As is well-known by people skilled in the art, the resistance is directly proportional to the length of the sensing channel. The resistance that the sensing channel 12B forms on the sensor 14B is apparently several times of the resistance that the sensing channel 12A forms on the sensor 14A. Such non-ideal characteristic may lead a subsequent controller to misjudge an intention of the user touch and thus trigger an erroneous operation result.
To minimize an average resistance difference of the sensing channels, a conventional solution usually adopts metal as the sensing channels to reduce an absolute difference between a maximum resistance value and a minimum resistance value. In the meanwhile, due to transparency requirements, the electrodes are mostly made of transparent indium tin oxide (ITO) rather than metal. It is understandable that, compared to one single material, production costs simultaneously involving two materials, such as metal and ITO, are higher. Further, metal is not a transparent material. In order to cover metal wires arranged around peripheries of electrodes, outer edges of a touch panel are forced to be a dark frame, which limits design flexibilities in the product appearance.